Method of testing a lead battery for the purpose of charging it under optimal conditions

ABSTRACT

Method of testing a lead battery for the purpose of charging it under optimal conditions, characterized in that it consists in testing the lead battery for the purpose of obtaining information relating to its condition by applying a test current and/or pulse thereto and by increasing the voltage at the battery terminals.

[0001] The present invention relates to charging lead accumulators andrelates more particularly to charging such accumulators with a free orimmobilized electrolyte.

[0002] It is desirable to determine the state of charge of a batterybefore even starting to charge it, in order, on the one hand, toestimate its residual capacity, which provides information on thepercentage of charge available and, on the other hand, to preventcharging a defective battery which could lead to irreversibly destroyingit.

[0003] Thus, determining the state of the battery is consideredessential for it to be recharged optimally under the best conditionswithout impairing its life or its nominal capacity according to thenumber of cycles. However, none of the chargers available on the marketprovide enough information allowing the state of the battery to becharged to be determined.

[0004] Several recharging profiles exist, but the latter do not reallytake account of the state of charge, they are mainly based on thereaction of the magnetic elements in relation to the voltage of thebattery in question since they use either leakage transformers (singleor double slope) or ferroresonant chargers whose output voltage isconnected to the change in voltage of the battery.

[0005] All conventional chargers (chargers operating at the 50 Hzelectrical engineering frequencies) generally have a preset timertriggered either at the first step or at the second step called V_(gas).However, if a battery is slightly discharged, charging takes placeduring the preset time interval which can then heat the batteryneedlessly. It is also a fact that maintaining the overcharge factoraccording to the percentage of discharge is not easy.

[0006] Several presently known techniques, due to the advances made inelectric vehicles and in the understanding of batteries, require thecharging voltage of each element or of each monobloc and its temperatureto be determined, this being so in order to determine possiblediscrepancies but also to offset the voltage according to temperature.

[0007] For the state of charge to be determined, it is necessary to haveavailable sophisticated electronics measuring all the most relevantparameters (voltages, current, temperature) in order to activate thecomputing algorithms so as to determine the available energy asdescribed in document FR-2 702 884 A1.

[0008] This approach, although valid within the context of an electricvehicle, is not justified in handling equipment when considering thecost of the necessary plant and equipment.

[0009] The methods of charging free electrolyte batteries are difficultto transfer to batteries with immobilized “gelled” electrolytes, sincethe transfer of energy, although identical at the start of charging fora discharged battery, becomes significantly different as soon as thebattery voltage reaches its degassing voltage “V_(gas)” which is anaverage 2.37 V/element at 30° C.

[0010] This is because, although the increase in voltage above V_(gas)can be tolerated for open lead batteries, it is highly inadvisable forsealed batteries (gelled or absorbed electrolyte battery) since anincrease in the potential means an evolution of gas which could lead toa deterioration in the battery or a loss of capacity.

[0011] However, as soon as an end-of-charge current of low value(variable between C5/100 and C5/200, instead of C5/20 and C/30 in thecase of free electrolyte batteries) is reached, an increase in voltageis then allowed without risk of damage, but with the voltage beinglimited to a value V_(max) (variable between 2.6 and 2.75 V/element).

[0012] Several charging profiles exist, those most commonly used beingWA, WOWa, WU, WUIa, IU, IUIa, etc. However, it is advisable to havesafety devices available such as charging time limiters depending on thevarious steps, voltage limiters, and capacity or even temperaturelimiters for conventional chargers not having a system available tocalculate the actual capacity of the battery being charged.

[0013] The most suitable profiles for recharging gel or free electrolytebatteries seem to be the WUIa or IUIa profile with, as a variant,control (amplitude, duration) of the end-of-charge current depending onthe technology employed, the desired charging time and the necessarycharging factor. The role of the end-ofcharge current Ia is also tohomogenize the electrolyte along the plate in order to allow theend-of-charge voltages of the elements which have not been able torecover their final voltages to reach equilibrium.

[0014] Example of the IUIa profile: the latter consists of threedifferent steps:

[0015] The first step of current I depends on the capacity of thebattery.

[0016] This current must be neither too big so as not to damage theelements, nor too small so as not to penalize the charging time of thefirst step and consequently the total charging duration:

[0017] the first possibility is to control the charger according to thebattery which is connected to it. However, batteries of differentcapacities cannot be connected to the same charger; consequently, thecharger becomes single capacity;

[0018] a second possibility consists in determining the capacity of thebattery and in matching the charging current to the capacity and to thestate of charge of the battery.

[0019] The second step of voltage U depends on the type of battery inquestion. Also, from 2.37 V/element at 30° C., the internal chemicalreaction is enhanced by electrolysis of water, thus creating anevolution of gas. This voltage is called the degassing voltage“V_(GAS)”. Thus, it is inadvisable to exceed this voltage for sealedbatteries otherwise the battery will be destroyed by evolution of gasoutside the elements.

[0020] The third step of current Ia depends on the technology of thebattery used; its amplitude and its duration depend on the capacity C5,on the discharge depth and on the desired charge factor.

EXAMPLES

[0021] 1) for a gel battery, the current Ia will have an amplitude ofbetween C5/100 and C5/200, and a duration of between 1 and 4 hoursdepending on the discharge depth and the required charge factor(typically the charge factor is about 1.05 to 1.07);

[0022] 2) for a free electrolyte battery, the current Ia will have anamplitude of C5/20 and C/30 and a duration of between 1 hour and 3 hoursdepending on the discharge depth and the required charge factor(typically about 1.15).

[0023] The object of the invention is to optimize the recharging ofbatteries of the two technology types (sealed and PbO) with the sameprinciples of calculating the capacity so as, on the one hand, todetermine the charging current as a function of the battery capacity,but also to optimize the recharging factor in order to prevent any riskof needless heating, and, on the other hand, to provide properrecharging whatever the initial conditions, with a minimum ofuncertainty by taking account of faults associated with the battery(deep discharge, unsuitable voltage, defective element, etc).

[0024] It also aims to obtain the best compromise for the overchargefactor/discharge factor, the temperature and the age of the battery soas to maintain the capacity of the battery during its life.

[0025] The object of the charging method is to improve the existingmethods which do not take into account the set of parameters making itpossible to optimize recharging. This guarantees full charging of thebattery without impairing its life. The method used for recharging leadbatteries with a liquefied electrode in addition comprises the profilefor a gel battery, current pulses which make it possible to obtain abeneficial effect on the life of the elements, but it also contributesto preventing premature losses of capacity as described in the article“T-AM et al, page 215, Journal of Power Source 53, 1995”.

[0026] The subject of the invention is therefore a method of testing alead battery for the purpose of charging it under optimal conditions,characterized in that it consists in testing the lead battery for thepurpose of obtaining information relating to its condition by applying atest current and/or pulse thereto and by increasing the voltage at thebattery terminals.

[0027] According to other characteristics of the invention:

[0028] it comprises a step of controlling the current by generating avariable-frequency function intended to produce a test cycle comprisingthe production of a current which increases up to a reference valuechosen according to the capacity of the battery, which is held for aspecific time defined by the capacity of the battery and which decreasessuch that there is significant excitation of the battery until a voltageclose to its degassing voltage or greater than this voltage is obtained.

[0029] The subject of the invention is also a device for testing a leadbattery, characterized in that it comprises a device for controlling thecurrent comprising a variable-frequency function generator intended toproduce a test cycle comprising the production of a current whichincreases up to a reference value chosen according to the capacity ofthe battery, then is held for a specific time defined by the capacity ofthe battery and decreases in such a way that there is significantexcitation of the battery until a voltage close to its degassing voltageor greater than this voltage is obtained.

[0030] According to other characteristics:

[0031] the device is a generator of current then of voltage with a largedynamic output range;

[0032] the current generator delivers a current of variable slopeaccording to the capacity of the battery.

[0033] The method and the associated device may be used in order toobtain information relating to the battery, for example the number ofelements, the remaining capacity of the battery and the discharge level.The device and the method may also detect defects before charging isstarted (battery not voltage-matched, damaged element). Thus, using thisdiagnosis, the battery will be charged better according to its statewhile storing deficiences during the charging cycle.

[0034] According to one embodiment of the calculation process usingcurrent pulses, of variable amplitude but of fixed duration, thisvariable amplitude depends on the reaction of the battery voltage. Thecalculation determines the current at the start of charging afterdiagnosis, before charging, is started, in order to prevent rechargingan unsuitable battery.

[0035] During this phase, which is common to both types of technology,the battery state of charge is determined after four to five series ofcurrent pulses. This number may vary depending on the battery type: forexample, for a gelled electrolyte battery, this number is for example 4,but for free electrolyte batteries, this number may for example exceed 5for high capacities.

[0036] The effects of the first group of pulses is to stimulate thebattery, and to prevent certain random phenomena associated with theelectrochemical process during reactions. The measurements forestimating the capacity will be made only after a certain time (the timeneeded to avoid the time constants of the chemical reactions of thepositive electrode, and of the negative electrode with the electrolyte).This delay in measurement for a time Tr also makes it possible to avoidtransient phenomena which could occur at the start of charging and causeerrors in measurement.

[0037] The invention will be better understood on reading the followingdescription, given solely by way of example and made with reference tothe appended drawings, in which:

[0038]FIG. 1 is a circuit diagram of a charging device fitted with thetest device according to the invention;

[0039]FIG. 2 is a graph showing the waveform of the charging currentsupplied during the test cycle and the battery voltage in reaction tothis current;

[0040]FIG. 3 is a graph of the control voltage in steps as a function oftime for a gel battery;

[0041]FIG. 4 is a graph of the battery charging current as a function oftime with the control voltage of FIG. 3;

[0042]FIG. 5 is a graph showing the maximum power curve;

[0043]FIG. 6 is a graph showing the variation of the loop width;

[0044]FIG. 7 shows the change in density as a function of the percentageof charge;

[0045]FIG. 8 shows a typical example of a profile comprising the methodaccording to the invention; and

[0046]FIG. 9 is a curve showing the change in the percentage of chargeas a function of the no-load voltage and the connection between thischaracteristic and that of the loop width.

[0047] The charger shown in FIG. 1 comprises a microprocessor 1, to afirst output of which is connected an adder 2 whose output is connectedto a converter 4.

[0048] A second output of the microprocessor 1 is connected to a circuitA for determining a reference current whose input is connected to thenegative terminal of the adder 2 and whose output is connected to theoutput of the converter.

[0049] A third output of the microprocessor 1 is connected to avoltage-generator circuit B.

[0050] The output of the circuit B is connected to a voltage terminal ofa battery 10.

[0051] The output of the converter 4 is connected to a current outputterminal of the battery 10.

[0052]FIG. 2 illustrates the waveform of the charging current which issupplied during the test cycle and the battery voltage in reaction tothis current. The current level I_(MAX) is controlled according to theactual charging capacity of the battery; for example the pulse currentlevel is equal to the capacity of the battery divided by N (where N isbetween 4 and 7 depending on the state of charge of the battery). Theslope of the positive and negative ramps has to be for example between20 and 40 A/s depending on the capacity of the battery. A slope ofdifferent value can be envisaged.

[0053] The duration of the constant current step is set at two seconds,but could be different.

[0054] The first group of current pulses is called the “conditioninggroup”; this agitates the electrolyte and prepares the battery toreceive the second group of pulses serving to record the voltagecharacteristics at the battery terminals.

[0055] During the pulses, the percentage of charge which will be storedafter 4 to 5 test cycles is calculated as an initial percentage of thebattery, but during these cycles the voltage-current characteristicswill not be taken since the risk of error is large for a highlydischarged battery. In order to prevent this risk, the behavior of thebattery voltage at zero current will be analyzed.

[0056] The battery voltage is constantly monitored during the test cycleso that it does not exceed the voltage V_(MAX), which would damage thebattery.

[0057] The pulse amplitude is therefore capped in case of overrun, toreturn the battery voltage to within the limits acceptable for thebattery.

[0058] After sending a current pulse of variable duration and amplitudeto the battery, the latter acts as an electrical circuit of the typeV_(batt)=E₀+RI, where R is the bias resistance, I is the excitationcurrent and E₀ is the no-load voltage of the battery.

[0059] Thus, by means of this pulse, an increase of the RI type iscreated which is superimposed on a capacitor-type charge by assumingthat the bias resistance remains constant for a measurement period.

[0060] The measurement period is characterized as described in FIG. 2.

[0061] Excitation Phase

[0062] 1) a linear increase of the type I=a t with a variable slopebetween 20 A/s and 40 A/s, it being possible for this slope to begreater depending on the capacity of the battery.

[0063] 2) a step with constant current of variable duration depending onthe capacity and state of charge of the battery.

[0064] 3) a linear decrease of the type I=−a t for the same slope as incase 1.

[0065] Relaxation Phase I=0

[0066] This phase has a fixed duration whatever the capacity ordischarge depth of the battery; it makes it possible to measure thevoltage V_(batt) at I=0 so as to determine the change in E₀.

[0067] The measurement is carried out as follows:

[0068] measurement of the no-load voltage in the excitation phaseE_(0(i,n−i)),

[0069] during the excitation phase, various values u_(i)(i_(i)) aremeasured,

[0070] measurement of the no-load voltage after an excitation phaseE_(o)(i,n) i,n ε N*₊ where i is the pulse rank and n is the number ofmeasurements.

[0071] These measurements will be used in various calculations whichwill be explained below.

[0072] Each measurement pulse makes it possible to provide a goodapproximation of the nominal capacity of the battery using thevoltage-current characteristics. During this pulse, the system storesthe voltages u₁(i₁) and u₂(i₂) obtained at respective currents i₁ andi₂. As can be seen in FIG. 2, these measurements are carried out in thepositive ramp of the measurement pulse. The evaluations of the voltageare not carried out directly at the battery terminals. It is necessaryto make a correction to compensate for the voltage drop in the powercables.

[0073] The calculation of the nominal capacity is based on the voltagevariation du=u₂(i₂)−u₁(i₁) in response to a current variation di=i₂−i₁,see FIG. 2. The term (du) is corrected in order to compensate for thevoltage present at the terminals of the power cables during theevaluation. For this, the parameters of the system must be set accordingto the following parameters.

[0074] b: experimental weighting coefficient (taking account of certainparameters connected to lead batteries).

[0075] Δu: voltage drop in the cable:

[0076] Δu=R*I where R is the resistance of the cable and

[0077] I is the charging current

[0078] N represents the number of elements constituting the battery.

[0079] The equation will be of the type:

C=b*di/[(N*du)−Δu)]

[0080] This calculated capacity will make it possible to determine thestarting current of the first step, a current which will subsequently beused to set the parameters for the charging process.

[0081] Thus, after the phase of estimating the capacity C5, the chargingcurrent depends on the acceptance of the battery. The latter is of theorder of the capacity C5/N (where N is a number between 4 and 7depending on the state of charge of the battery and C5 is the capacitywhich could be supplied by the battery in 5 h, that is to say 100% ofthe battery capacity).

[0082] To start charging, the battery voltage is raised when the chargeroutputs its nominal current. This voltage becomes the reference valuefor controlling the voltage V_(reg). V_(reg) changes with a fixed periodbut with a variable amplitude. The amplitude of the voltage V_(reg)depends on the change in the state of charge of the battery. The morethe battery is charged, the more the value of the control voltageV_(reg) decreases.

[0083] Thus, during the control period, if the charging current isgreater than the control current, there will then be an increase in thevoltage of the battery with respect to the voltage V_(reg), which,through the control loop, will make it necessary to adjust the chargingcurrent such that the battery voltage is constant over the controlperiod and equal to V_(reg) as shown in FIGS. 3 and 4.

[0084] As for FIG. 3, it shows an example of an application to a gelbattery where the control voltage is set by steps of different value,but of fixed duration depending on the change in the total voltage ofthe battery.

[0085] Increasing the voltage in steps makes it possible to control thestate of charge of the battery better, and to be able to gauge theacceptance state of the latter, since if, for a given voltage controlstep, the battery voltage diverges from that of V_(reg), this means thatthe charging current is not matched to the charge acceptance of thebattery, and, consequently, there will be a decrease in the currentuntil a battery voltage which agrees with the change in Vreg isobtained.

[0086] From then on, the charging profile becomes completely dependenton the change in the control voltage, and, consequently, it can adaptitself according to the behavior of the battery voltage subjected to acharging current. The charging principle which has just been describedmay be just as valid for charging sealed batteries as for those with anopen electrolyte, and, as a result, it is distinguished from theconventional type-IUIa profile.

[0087] Thus, by supplying, for example in the context of a gel battery,a reference step at voltage V_(reg), the latter makes it possible tokeep the control current during the charging phase at a value close tothe maximum current tolerated by the battery, depending on its chargingcapacity up to a voltage per element of for example between 2.3 and 2.42V depending on the temperature of the electrolyte in the battery.

[0088] After this common phase of estimating the capacity, and ofcontrolling the voltage V_(reg), there are two distinct variants forrecharging lead batteries.

[0089] Variant 1: Charging a free electrolyte battery.

[0090] the voltage of the battery is measured before the measurementpulse (E_(0(i,n−1))) and after the latter (E_(0(i,n))) at a currentequal to zero. These two voltages correspond to the difference inpotential of the voltage-current characteristics of the battery.

[0091] The difference between these two voltages gives the differenceW_(i) (loop width)=E_(o(i,n))−E_(0(i,n−1))). This difference ischaracterized by a change in the voltage of the battery reflecting thechange in the state of charge. The loop width E_(0(i,n))−E_(0(i,n−1)) isrepresentative of the charge level of the battery.

[0092]FIG. 5 shows the start of energy transfer in the case whereacceptance of the battery seems to be identical for the two leadtechnologies (sealed, PbO) and where the efficiency of the energytransfer is maximum in the region Di (initial region); the loop width isvirtually zero (high bias resistance). This figure also shows thecharacteristics of the completely charged battery in the region close toDf (final region), a region in which the change in voltage of thebattery is virtually constant within a given current range, thendecreases rapidly. The change in characteristics v(i) for a batterycharged during measurement and electrical agitation pulses is locatedclose to the saturation zone, which zone could have a harmful effect onthe battery if the latter is kept in this charging space, since therewould be losses of water by electrolysis and a temperature increase.Also, this zone can be explored without risk by measurement pulseshaving a very short duration with respect to the normal chargingprocess.

[0093] To avoid saturation phenomena in the V, I plane, a maximum outputpower that is not to be exceeded during the normal charging cycle isnecessary, such that whatever the test or analysis cycle, the operatingpoint will remain inside an allowed zone.

[0094]FIG. 6 shows the variation in the loop width during charging. Itis virtually zero for most of the charging. It increases suddenly onapproaching 100% charge to reach a maximum value, then decreasesslightly. This sudden increase is explained, on the one hand, by thethermal agitation due to the electrolysis of water for the PbO batteriesand, on the other hand, by an increase in the resistance to the flow ofelectrons in the various layers (Pb, PbO₂ and H₂SO₄) and a reduction inthe bias resistance.

[0095] The system driving the charger calculates the slope at eachmeasurement pulse and determines whether the maximum has been reached,in which case 100% charging has been attained.

[0096] The method for calculating the percentage of charge makes itpossible to estimate the current to be injected at each period ofcontrolling the control voltage during the first charging step. Thecontrol period can be varied according to the capacity of the battery tobe charged and its percentage of charge. In the present application, itwill be, for example, about 6 minutes.

[0097] It should be recalled that charging the battery consists of asuccession of phases of energy transfer and of measurement pulses ofmarkedly shorter duration. Similarly, the characteristics of the batteryare determined during these measurement pulses.

[0098] The method of bringing the measurement pulses closer together isbased on calculating the percentage of charge. The more the latterincreases, the more it is necessary to readjust its calculationaccording to two principles:

[0099] increasing the frequency of the measurement and agitation pulses;in the present application this frequency is multiplied by two;

[0100] rebalancing the calculation equations according to the change inthe no-load voltage.

[0101] However, the measurement pulses must not be too close together atthe risk of having variations which are too small, of one measurementpulse over the following pulse, and thus of considering the battery tobe totally charged.

[0102] The frequency of the current pulses directly affects the estimateof the percentage of charge and also the change in the densitycharacteristics of the electrolyte.

[0103] This is because the high current levels of these pulses createelectrical agitation of the electrolyte, an agitation which makes itpossible to obtain good homogeneity of the sulfuric acid H₂SO₄ densityalong the plates in order to avoid stratification phenomena but also asignificant reduction in water consumption and the reduction of thecharge factor. This variable-frequency electrical agitation depends onthe state of charge of the battery. Its change is connected to thecalculation of the percentage of charge. The closer the latter is to100% of the state of charge, the more the frequency increases so as toagitate the electrolyte better and to allow a reduction in the waterconsumption and an optimization of the charge factor (the typical chargefactor for a free electrolyte battery discharged to 80% is about 1.15 toobtain a density of 1300 at 30° C. making it possible to have a fullycharged battery; as a result of the electrical agitation, the chargefactor is reduced to 1.08-1.10 giving a density of 1300 at 30° C. and acompletely charged battery). An example is thus supplied by FIG. 7showing the change in density as a function of the percentage of charge.

[0104] In addition, the electrical (ionic) agitation has a beneficialeffect on battery aging as described in the article-.T-AM et al., page215, Journal of Power Source 53, 1995. A typical example of a profilecomprising this method is shown in FIG. 8.

[0105] It is these measurement pulses which are at the base of thismethod. This is because, at the start of each measurement pulse, that isto say when the current delivered becomes equal to zero, the batteryvoltage is increased. From this voltage, called the battery relaxationvoltage, the correspondence with different charge levels is establishedusing a table pre-established following several tests. This provides theinformation concerning the effective charge level of the battery.

[0106] As the energy transfer continues, the charge level may bedetermined using a measurement pulse.

[0107]FIG. 9 is the curve showing the change in percentage of charge asa function of the no-load voltage, and the connection between thischaracteristic and that of the loop width. Thus, using these twocharacteristics, the change in charge is controlled better bycontrolling its charging current.

[0108] The initial and final (100%) percentages of charge also make itpossible to set the end-of-charge current depending on the capacity ofthe battery and consequently to optimize the charge factor according tothe criteria of the battery manufacturers.

[0109] Once the battery is completely charged, the maintenance chargingphase is activated, depending on the calculated end-of-charge current,in the form of a pulse. A charge profile example is appended in FIG. 8specifying the shape of the curve, and the presence of calculation andelectrical (ionic) agitation pulses.

[0110] Variant 2: Charging and gel battery

[0111] The IUIa profile for a gelled electrolyte battery isdifferentiated mainly in its second and third phases compared to thatfor the free electrolyte battery.

[0112] This is because, as has been mentioned in the preamble, it isnecessary to take certain precautions when recharging gel batteries,such as the strict compliance with the control voltage (in this casethis is 2.37 V/element at 30° C.), but also compliance with theend-of-charge current and with its duration.

[0113] The charging method thus defined makes it possible to charge asealed (gel) battery under the best conditions for the battery. Thismethod makes it possible to recharge various capacity ranges (capacitylimited only by the output power of the charger) without any adaptation,since the method will automatically adapt its charging process to thecapacity of the battery and to its discharge depth, thus avoiding anyabnormal heating of or risk of damage to the battery.

[0114] The means stated above thus make it possible to provide, via acharger with a large dynamic range, the possibility of charging varioustypes of battery technologies, voltages and capacities and as a resultto have a charger with a multivoltage functionality (for example acharger may charge a battery of 24 V or 36 V or 48 V without anyoperator intervention) and multicapacity functionality (the same chargermay charge a battery of 250 Ah or a battery of 600 Ah without anyoperator intervention).

1. Method of testing a lead battery for the purpose of charging it underoptimal conditions, characterized in that it consists in testing thelead battery for the purpose of obtaining information relating to itscondition by applying a test current and/or pulse thereto and byincreasing the voltage at the battery terminals.
 2. Method according toclaim 1, characterized in that it comprises a step of controlling thecurrent by generating a variable-frequency function intended to producea test cycle comprising the production of a current which increases upto a reference value chosen according to the capacity of the battery,which is held for a specific time defined by the capacity of the batteryand which decreases such that there is significant excitation of thebattery until a voltage close to its degassing voltage or greater thanthis voltage is obtained.
 3. Method according to claim 2, characterizedin that it comprises a step of calculating the percentage of chargemaking it possible to estimate the current to be injected at each periodof controlling the control voltage during a first charging step. 4.Method according to claim 3, characterized in that the control processvaries according to the capacity of the battery to be charged and itspercentage of charge.
 5. Method according to one of claims 2 to 4,characterized in that at the start of each measurement pulse, when thecurrent delivered to the battery becomes equal to zero, the batteryvoltage is increased from this voltage called the battery relaxationvoltage, the correspondence with different charge levels is establishedusing a table pre-established following several tests and informationconcerning the effective charge level of the battery is thus obtained.6. Device for testing a lead battery, characterized in that it comprisesa device for controlling the current comprising a variable-frequencygenerator (1, 2, 4) intended to produce a test cycle comprising theproduction of a current which increases up to a reference value chosenaccording to the capacity of the battery (10), then is held for aspecific time defined by the capacity of the battery and decreases insuch a way that there is significant excitation of the battery until avoltage close to its degassing voltage or greater than this voltage isobtained.
 7. Device according to claim 6, characterized in that itcomprises a generator of current (A) then of voltage (B) with a largedynamic output range.
 8. Device according to claim 7, characterized inthat the current generator (4, A) delivers a current of variable slopeaccording to the capacity of the battery.
 9. Device according to one ofclaims 6 to 8, characterized in that it comprises a system (1) drivingthe charger which calculates the slope of the current at eachmeasurement pulse and determines whether the maximum has been reached,resulting in 100% charge.